1. Field of the Invention (Technical Field)
The present invention relates to air handling units, such as which move large volumes of air with motor-driven fans, and relates particularly to sound-attenuation components for such units, and specifically to movable sound attenuating baffles for air handling units.
2. Background Art
Custom air handling units (AHU) are mechanical equipment that deliver tempered and/or filtered air (via ductwork) to a building or portions of its interior space. FIGS. 5 and 7 of the drawing figures depict the general layout of an air handling unit conventional to the art. Because the one or more fans 20 contained within the AHU to move the air can be quite noisy, it is common to install a bank of passive sound-attenuating baffles 10 between the fan(s) 20 and the intake or discharge port (or both) of the AHU as needed. The baffles 10 may either be self-supporting members arranged parallel to each other, or an array of modules that, like a filter bank, fill the interior cross-section of the AHU's airflow-conveying tunnel. Each baffle 10 has a rectangular, flat-oval or teardrop-shaped chord profile of some thickness, and the baffles are positioned so that the spacing between them is a predetermined distance. The sound attenuating performance of these baffles 10 depends on this distance or “passage width”, the baffle thickness, the baffle length and its materials.
Typically, an individual baffle is composed of acoustically absorbing glass fiber batting fill, surrounded by a perimeter flow-facing skin of perforated metal that conforms to the desired chord profile and protects the fill. To separate the fill from the gas flow, without unduly impeding the transmission of sound from the flow into the acoustically absorbent media, an additional impermeable thin film sometimes is placed between the glass fiber and the perforated metal. Like filter banks, heat transfer coils, and other common components installed serially within the AHU air tunnel, these baffles or “sound traps” are—with respect to an AHU operating normally—permanent, immobile fixtures that occupy a fraction of the AHU's footprint.
In the marketplace for heating, ventilation and air-conditioning (HVAC) systems where such custom AHUs are engineered and sold, the size of an AHU's footprint can have a direct impact on its cost and likelihood of being selected. Hence, the smaller the footprint, the more competitive (from a commercial standpoint) a custom AHU becomes.
An AHU footprint is occupied by the physical lengths of the components and clearances reserved to enable access for component inspection, service and removal. For instance, one will usually find, at a minimum, a two-foot-long clear section upstream of a filter bank. This allows maintenance personnel to access individual filter modules and, if needed, replace dirty ones with clean modules.
In the case of sound traps positioned immediately downstream of a belt-driven fan 20, it is customary to reserve approximately two feet (or more) of AHU length between the belt-drive assembly and the intake side of the sound trap including the baffles 10 (FIG. 7) This permits convenient walking clearance around the fan-drive assembly 20. On the downstream side of the sound traps, there is usually a clearance of two or more feet to allow efficient diffusion of airflow discharging from the passages between parallel baffle surfaces. Without this downstream clearance during AHU operation, the aerodynamic resistance of the sound traps (and that of serially adjacent airflow-conveying components) tends to increase. Thus, industry practice maintains this clearance downstream of sound traps within an AHU.
But because the downstream clearance only impacts AHU performance when it operates, such a clearance is not required when the AHU is off and undergoing inspection or maintenance. This space can be used alternatively, as described herein.